1. Field of the Invention
The invention relates to furniture structures, in particular tables, and concerns an improved supporting structure for a table top, having a buttress arrangement coupling the table top to the legs, preferably with stiffening members disposed between the legs and spaced from the underside of the table top.
2. Prior Art
In tables, desks and similar articles of furniture having a horizontal member supported by legs, joint structures couple the horizontal member or table top to the legs in a manner that holds the legs stationary relative to the table top, usually with the legs aligned perpendicular to a horizontal table top, but also sometimes at an angle relative to vertical. An example is a horizontal rectangular table top having four legs, but other numbers of legs and other configurations for the top are also possible. To hold the table top steady, the joints between the top and the legs need to resist angular displacement of the legs relative to the top, which would allow the table top to wobble.
The legs are usually braced by members that extend laterally from the legs and couple the legs to the table top and/or to the other legs. In one arrangement, the legs are fixed endwise to the underside or edge of the table top, and linear horizontal members spaced well below the table top extend between the legs, either parallel to an edge of the table top or diagonally. The linear members spaced below the table top may interfere with foot or knee room under the table, and insofar as the structures formed are rectangular, they are not well braced against deflection in the manner of a parallelogram.
To provide a more stable structure, diagonal braces can extend from a point on the leg spaced below the underside of the table to a point on the underside of the table spaced from the joint between the top end of the leg and the table top. The diagonal braces typically reside parallel to the plane of the edge of the table top, but could also extend inwardly, for example, diagonally under the table top. Preferably, two diagonal braces are provided in perpendicular planes.
A variation of this is a flange member attached along the underside of the table top, abutting endwise against two legs at a vertical position immediately adjacent the table top. The flange member provides diagonal bracing to an extent that depends on the vertical dimension of the flange member. In many tables, the flange members between the legs form a downwardly opening box attached to the underside of the table top having a depth, for example, of several inches.
The bracing members can be wood, metal or the like, metal bracings and fittings being convenient for attachment and strength. In traditional table structures, an attempt is made to conceal the joint structures between the table top and the legs. Especially where the leg/top joint includes a metal fitting connecting between the leg and the underside of the table top, the metal fitting is generally made inconspicuous. This is for aesthetic and economic reasons. Metal is cold and industrial in appearance, and is generally not preferred for residential or office use. Concealing the fastening and/or bracing structure also eliminates some finishing details, which saves production costs.
However, metal furniture assembly fasteners are strong and durable, and generally can be attached to the underside of a horizontal planar support and/or the inside surface of the side supports using simple screws or bolts. The leg constructions and fasteners structurally work independently of one another, typically being weakest at the points where they are attached. Several types of metal fasteners used in combination with wood members have been proposed. For example, U.S. Pat. No. 1,876 336--McLaughlin discloses a sheet metal corner plate attached to a leg by a series of bolts and to side supports by screws. The horizontal planar surface is in turn secured to the side supports by screws. The plate height is equal or less than the height of the side supports such that the corner plate is substantially concealed. The use of screws to attach the side rails and the horizontal planar surface produces a connection that can work loose over a relatively short time. Although the plate is concealed behind the side supports, its height is thereby limited, which reduces the structural moment resistance against deflection of the joint due to forces applied at the opposite end of the leg. It would be desirable to enable attachment of a triangular bracing structure at a point spaced from the joint between the leg and the horizontal surface, without producing aesthetic and structural drawbacks.
U.S. Pat. No. 5,163,373 to Anderson et al. (1992) discloses an elongated metal leg construction adapted to receive a decorative wood cover piece and a metal top plate for connection to the underside of the horizontal planar surface. Reliance on screws to attach the side rails to the horizontal planar surface and the metal top plate to the horizontal planar surface likewise produces a connection that can work loose at the connection points. The large number of pieces and the attention required for the various connections produces a relatively expensive leg construction. Furthermore, the metal gusset plates used to stabilize the leg portion are concealed behind the side supports therefore are of limited height and limited structural moment resistance. Each top plate and leg construction resists the structural moment forces applied along its respective leg independently of the other legs. As a result, extreme pressure can be applied to the screw connections, which are prone to loosen, requiring repair or replacement.
Metal leg members attached by metal fasteners (e.g., screws) to the legs and to the underside of the table top, although usually hidden, can be lengthened such that the diagonal stabilizing members attach lower on each leg and are visible. This improves structural rigidity by reliance on triangulation at the corners. The three members of a triangle are provided by the table top, a diagonal supporting brace (or two braces in perpendicular planes), and an upper portion of the leg between its end attached to the table top and a point of attachment to the brace. The traditional side supports can be eliminated. Various details for the brace and the leg are possible in an effort to create a contemporary aesthetic look. However, in each case the leg extends upwardly to an attachment to the underside of the horizontal planar surface for achieving triangular bracing, and the bracing structure and any fasteners and fittings, are difficult to resolve aesthetically with the table structure. The bracings of fasteners are often therefore aesthetically distinct from the basic table structure and are prominent elements of the appearance of the article of furniture. It would be desirable to merge more effectively the aesthetics of the table and the bracing structures employed.
Bracing designs and fasteners also often involve an excessive number of parts and/or manufacturing operations for assembling parts. Several types of metal fasteners with metal legs have been proposed. U.S. Pat. Nos. 2,822,228--Comer; U.S. Pat. No. 3,366,357--Rudow; and U.S. Pat. No. 3,816,269--Lang disclose examples of techniques attempted for reducing the expense or improving the aesthetics of a fastener and bracing means extending a structurally sufficient distance down the legs. However, there are several problems. The fasteners are connected to the horizontal planar surface with screws that define bracing attachment points that are critical and may weaken with repeated movement. The connection spaced from the top end of the leg provides bracing triangulation for structural stability but the spacing is minimal, which limits such stability. The connection at the leg also defines a critical attachment point that may weaken. There are minimal or no intermediate supports which could distribute the structural moment forces generally among the legs, braces and fasteners.